In a conventional boiling water nuclear reactor, a pressure vessel contains a reactor core submerged in water. An annular shroud surrounds the reactor core and is spaced radially inwardly from the sidewalls of the pressure vessel to define a relatively narrow downcomer therebetween. Various other components are also found in the pressure vessel and provide considerable congestion therein.
Conventional fasteners in the form of nuts and bolts are used in reactor assemblies, repairs, and modifications, with the nut typically requiring effective locking to the bolt in order to prevent its liberation therefrom. Typically the nuts are lock welded directly to the bolt. Since bolts are typically located underwater in the pressure vessel and with limited available access thereto, maintenance personnel typically must assemble and lock the bolts and nuts remotely, and remotely weld the nuts to the bolts, which is a difficult process.
In one exemplary reactor, a circular plug of material was removed from the core shroud by conventional electrical discharge machining (EDM) for subsequent metallurgical analysis. The remaining aperture in the shroud was plugged using a plug bolt and nut for preventing flow of water through the aperture. In view of the limited access in the vicinity of the aperture in the shroud, an improved fastener design was desired for allowing the bolt and nut to be installed remotely, with the nut being locked to the bolt without the need for conventional welding thereto.